radiator can be reduced to 15mm diameter provided
the run is no further than 300mm (12”) away from
the 22mm gravity circuit. No thermostatic or manually
adjusted valves should be fitted to the heat leak
radiator to ensure that it can never be shut down. If
a thermostatic control over-heat valve, which controls
the flow when the water in the hot water cylinder
has reached a predetermined unsafe temperature, is
specified as part of the system then you must ensure
that the heat leak radiator has a rating to cope with
the extra demands made on it when the hot water
cylinder is isolated.
Adjustable circulating pump
It is important that the system flow can be adjusted
via the circulating pump to ensure the best operation.
A system flow which is too slow could potentially
over-heat or at the very least take a long time to
warm the house. One that is too fast could reduce the
time it takes for the water pass through the boiler and
absorb heat, thus reducing the overall effectiveness
of the system. Ensure that isolation valves are fitted
on either side of the pump to allow for easy pump
maintenance and safe removal in the event of a fault.
Allow a minimum of 1.5 metres (5’) of static head and
always follow the pump manufacturer’s instructions.
Electrical connections to the pump, like the stove
installation itself, are subject to current Building
Regulations.
Electrical connections
Electrical connections to the circulating pump,
motorised valves or link-up components are subject to
Building Regulations compliance and must be carried
out by a qualified electrician or by a person registered
with the appropriate Competent Person scheme. In
England and Wales building regulations Approved
Document P sets out the overall criteria and
requirements to ensure electrical safety and
have been
introduced to help reduce the number of deaths,
injuries and fires caused by faulty installations.
Mains water connection
In order to safeguard water quality and public health,
when connecting the boiler stove heating system to
the mains water you must ensure that the connection
complies with all local water authority regulations. A
legal duty is placed on all users, owners or occupiers
and anyone who installs plumbing systems or water
fittings to ensure that they are installed and used in
accordance with UK Water Supply (Water Fittings)
Regulations 1999.
Gravity circuit pipework
Motorised valves fitted in the gravity circuit pipework
must be configured to revert to the open position
should the power fail. In addition the hot water
cylinder and heat leak radiator should be positioned
as near to vertically above the boiler stove as possible
and with sufficient height to encourage the natural
flow. Any horizontal runs in this pipework should be
inclined, again to encourage the natural flow.
High and low limit thermostats
A high limit over-heat thermostat set at 80ºC should
be fitted to the gravity flow pipework and connected
to the circulating pump so that should the system
temperature exceed 80ºC then the pump will
automatically be switched on. This safety precaution
will ensure that the gravity circuit does not overheat.
A low limit thermostat set at 45ºC should be fitted
to the gravity return pipework and connected to the
circulating pump. This should be set to come on when
the water temperature reaches above 45ºC to begin
the circulation process.
Hot water cylinder
This should be fitted with a thermostatic control
valve which turns off the flow when the water in the
cylinder has reached a predetermined temperature.
If your boiler stove is part of a new heating system
this is now a building regulations requirement. You
must ensure that this water setting is not too hot
to use, especially if there are children in the house.
A temperature set at 60ºC or just slightly above is
recommended. Please note that temperatures below
60ºC may encourage the growth of harmful bacteria
such as legionella.
During commissioning, as the thermostat may not
be accurate, it is important that after the system has
been operating for at least three hours the hot water
temperature is tested at the tap closest to the hot
water cylinder to ensure that it will not scald children
or the elderly who use it. It is important that the heat
leak radiator is specified with a rating to cope with
the extra demands made on it when the hot water
cylinder is isolated from the system.
Thermostatic radiator valves (TRVs)
The UK’s Domestic Heating Compliance Guide
stipulates that any new heating system is temperature
zoned. For properties with a floor area of less than
150m2 (which includes most UK homes) this can really
only be achieved by incorporating TRVs. However, two
radiators on the pumped central heating circuit should
not have TRVs fitted, as they will be needed to allow
any excess heat to safely dissipate should the over-
heat thermostat switch on. Please note these radiators
could become excessively hot and we therefore
recommend that these two at least should be of
the low surface temperature type to help prevent
accidents.
System Balance
See the section on the importance of ensuring
that your heating system is correctly balanced. An
unbalanced system is inefficient and therefore costly
to run. See page 26
22
